1. Field of the Invention
This invention concerns apparatus for fixation, dessication, and embedding of biologic specimens.
2. Description of the Prior Art
In most cases biologic specimens cannot be examined directly in a microscope, especially an electron microscope, but require prior treatment.
Generally such pretreatment consists primarily in stabilization of vital structures by suitable chemicals (fixation, for example, by aldehyde and/or heavy metal compounds in aqueous solution) or by rapid freezing (cryofixation) in subsequent dessication in organic solvents (for example acetone or aldehyde, under certain circumstances with the addition of heavy metal compounds to increase contrast in the electron microscopic image or to stabilize the structures after cryofixation) and finally, in impregnation with materials (embedding, for example, in wax or plastic) which support the specimen while it is being cut into a thin or ultra thin section by a microtome or ultra microtome. This process generally requires, on the one hand, repeated changing of different liquid media. On the other hand, it must be carefully observed that the specimen surfaces are always in contact with fresh liquid since otherwise the desired exchange of cellular or tissue liquids within the specimens vis-a-vis the different treatment liquids proceeds too slowly. In many cases, incubation is carried out, in addition, at reduced temperature (reduction of autolytic reactions during fixation or reduction of the production of specimen inherent structures during dehydration) or at increased temperature (reduction of viscosity of embedding media or melting of the wax used for embedding).
This preparation process can accordingly, be carried out by hand, however, it requires continuous monitoring and an altogether very high expenditure of work by manual filling, refilling, shaking, or additionally, by placement of the tank in the cooling or heating devices. With regard to optimum reproducibility of results and in view of continuously rising labor costs, automatic apparatus ("tissue processors") have been developed which carry out the entire treatment process automatically and reproducibly. Such automatic apparatus can be obtained commercially in numerous different designs for purposes of light and electron microscopy and is used primarily in larger laboratories or for repetitious work. One existing apparatus includes a treatment compartment in which holders for the biologic specimens to be treated can be stacked one on top of the other in columnar form. The holders are liquid permeable by means of porous inserts on the bottom and top and the apparatus includes a device to generate periodic raising and lowering of the liquid level in the treatment chamber so that the specimens in the tanks are flushed. Due to high costs as well as, to some extent, relatively high consumption of fixation, dessication, and embedding materials, such automatic devices have, however, only been used in limited areas. In all other sectors, the manual approach is still most common, aside from rotary discs to generate continuous weak convection of the treatment media. The manual labor which consists at least in changing of the different media treatment liquids which are necessary in small time increments of 10 to 20 minutes each, frequently with additional shaking, and last but not least, cleaning of the different vessels is not desirable due to the fact that the liquids most frequently used, fixation solutions, intermediate, and dessication liquids, as well as some embedding materials are hazardous to health and either come into contact with the skin (allergic reactions) or may be inhaled (general injury). This aspect necessitates additional precautionary measures which further complicate work.
The objective of this invention is thus, to design a treatment apparatus which is relatively simple and thus considerably below the costs of the aforementioned automatic apparatus in terms of purchase price, consumption of fixation, dessication, and embedding liquids which do not exceed amounts used in purely manual liquid replacement, which however, precludes or minimizes skin contact with the liquids used as well as the risk of inhalation of toxic vapors. Thus, this treatment apparatus is designed to simplify the aforementioned preparation steps to a degree comparable to that of automatic equipment and, moreover, be at least functionally on par, i.e., relative to preparation effect. However, in spite of simple structure, the treatment apparatus should be receptive to additional control equipment for providing convenience and automation.